Modulation device and pulse wave generation device

ABSTRACT

Provided is a modulation device including a signal selection circuit selecting two carrier signals from a plurality of carrier signals having the same frequency and the same phase difference according to a defined control signal and outputting the selected carrier signals, and a phase interpolator adjusting the phase in smaller units than the phase difference between the plurality of carrier signals according to the control signal and modulating the frequency or the phase of the carrier signal into a baseband signal based on the carrier signals selected by the signal selection circuit to generate a carrier wave signal.

TECHNICAL FIELD

The present invention relates to a modulation device provided in awireless communication apparatus to modulate a frequency or a phase of acarrier signal according to a baseband signal, and a pulse wavegeneration device using the same.

BACKGROUND ART

A lot of wireless communication apparatuses use a frequency modulationmethod or a phase modulation method as a data modulation method. Thewireless communication apparatus employing such modulation methodstransmits and receives a carrier wave signal generated by increasing ordecreasing the frequency of a carrier signal by a fine frequencyaccording to data (baseband signal). Here, the frequency of the carriersignal is referred to as carrier frequency fc and the fine frequency isreferred to as modulation frequency Δfc.

A conventional frequency modulation device having a structure as shownin FIG. 1 has been widely used. The frequency modulation device of FIG.1 includes carrier signal generator 1 generating a carrier signal,digital-analog converter 2 converting a baseband signal which is adigital signal into an analog signal, bandwidth limiting filter 3reducing harmonic components contained in the baseband signal outputfrom digital-analog converter 2, and analog mixer 4 mixing the outputsignal of bandwidth limiting filter 3 with the carrier signal outputfrom carrier signal generator 1, and increasing or decreasing thefrequency of the carrier signal by a fine frequency according to thebaseband signal to output a carrier wave signal.

The conventional frequency modulation device of FIG. 1 has disadvantagesin that the circuit area increases due to bandwidth limiting filter 3,etc. and power consumption increases due to a large stationary currentflowing through analog mixer 4.

A method for converting frequency of an input signal without usinganalog mixer 4 has been disclosed in e.g., International PublicationPamphlet No. 06/030905 (hereinafter, referred to as Patent reference 1).Patent reference 1 suggests a structure for shifting the phase of aninput signal in every period using a phase interpolator to convert afrequency of the input signal. FIG. 2 shows a configuration example ofthe phase interpolator.

As illustrated in FIG. 2, CLK(i) and CLK(i+1) having the same frequencyand different phases and a phase modulation control signal (digitalsignal) output from a control circuit (not shown) are input to phaseinterpolator 5.

Phase interpolator 5 divides time T equivalent to a phase differencebetween CLK(i) and CLK(i+1) by b:a(a+b=N) according to set value b inputas the phase modulation control signal and outputs a signal delayed fromCLK(i) by time (b/N)×T equivalent to set value b.

In detail, when a=4, b=3, the phase of CLK(i) is −135° with respect to areference clock and the phase of CLK(i+1) is −180° with respect to thereference clock, since phase difference T between CLK(i) and CLK(i+1) is45°, phase interpolator 5 outputs a signal delayed from CLK(i) by(3/7)×45°, i.e., a signal having a phase of −154°.

FIG. 3 illustrates a configuration example of a conventional frequencyconversion device using phase interpolator 5 of FIG. 2. FIG. 3illustrates the configuration described in above Patent reference 1.

As illustrated in FIG. 3, the conventional frequency conversion deviceincludes m phase generation circuit 10, n phase generation circuit 20,and single phase clock generation circuit 30.

m phase generation circuit 10 outputs m phase clock signals havingfrequency fc/m and phase differences at equal intervals using a clocksignal having frequency fc.

n phase generation circuit 20 includes n phase interpolators 5 shown inFIG. 2 and generates n phase clock signals having the same phasedifference from the m phase clock signals generated in m phasegeneration circuit 10. That is, n phase generation circuit 20 outputs nphase clock signals having a period of (m/fc)×(1/n).

Single phase clock generation circuit 30 synthesizes the n phase clocksignals output from n phase generation circuit 20 and outputs a singlephase clock signal having a frequency of fc×n/m.

The frequency conversion device of FIG. 3 does not need analog mixer 4and bandwidth limiting filter 3 shown in FIG. 1. In addition, when n andm are set to satisfy n/m=(fc+Δfc)/fc, a carrier signal having afrequency of fc can be converted into a carrier wave signal having afrequency of fc+Δfc.

In general, the carrier frequency used in the wireless communicationapparatus ranges from a few hundred MHz to a few GHz and the modulationfrequency used in the wireless communication apparatus ranges from a fewten KHz to a few MHz. Thus, when the frequency conversion device of FIG.3 is employed in the wireless communication apparatus, if n and in areset to satisfy n/m=(fc+Δfc)/fc, n and m have very large values.

Accordingly, the size of the m phase generation circuit or the n phasegeneration circuit increases. In particular, the n phase generationcircuit needs a lot of phase interpolators. Therefore, the frequencyconversion device of FIG. 3 has disadvantages such as large circuit areaor high power consumption.

As a result, the wireless communication apparatus, which is sorely inneed of miniaturization or low power consumption, may not use thefrequency conversion device of FIG. 3 as the frequency modulation deviceor as the phase modulation device.

SUMMARY

Therefore, an object of the present invention is to provide a modulationdevice which has features such as small circuit area and low powerconsumption and which can modulate a frequency or a phase of a carriersignal according to a baseband signal, and a pulse wave generationdevice having the modulation device.

According to an aspect of the present invention for achieving the aboveobject, there is provided a modulation device for modulating a frequencyor a phase of a carrier signal into a baseband signal, the modulationdevice including a signal selection circuit selecting two carriersignals from a plurality of carrier signals having the same frequencyand the same phase difference according to a defined control signal andoutputting the selected carrier signals, a phase interpolator adjustingthe phase in smaller units than the phase difference between theplurality of carrier signals according to the control signal andmodulating the frequency or the phase of the carrier signal into thebaseband signal based on the carrier signals selected by the signalselection circuit to generate a carrier wave signal, and a phasemodulation signal generation circuit generating the control signal tocontrol the signal selection circuit to select the two carrier signalsand the phase interpolator to generate the carrier wave signal.

According to another aspect of the present invention, there is provideda pulse wave generation device including an S phase clock convertercircuit having S sets of a signal selection circuit and a phaseinterpolator and outputting S carrier signals having the same frequencyand a phase difference of 360°/S, and a duty ratio converter circuitgenerating S carrier wave signals having different duty ratios in unitsof 1/S from the S phase carrier signals output from the S phase clockconverter circuit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a configuration example of aconventional frequency modulation device.

FIG. 2 is a schematic diagram illustrating the configuration andoperation of a phase interpolator.

FIG. 3 is a block diagram illustrating a configuration example of aconventional frequency conversion device.

FIG. 4 is a block diagram illustrating the configuration of a modulationdevice according to a first exemplary embodiment.

FIG. 5 is a circuit diagram illustrating a configuration example of aphase interpolator of FIG. 4.

FIG. 6 is a timing diagram illustrating an operation example of thephase interpolator of FIG. 5.

FIG. 7 is a block diagram illustrating a setting example of phasemodulation control signals supplied to a signal selection circuit andthe phase interpolator of FIG. 4.

FIG. 8 is a timing diagram illustrating a detailed operation example ofthe signal selection circuit and the phase interpolator of FIG. 4.

FIG. 9 is a timing diagram illustrating a phase modulation operationexample of the modulation device according to the first exemplaryembodiment.

FIG. 10 is a timing diagram illustrating a detailed operation example ofa modulation device according to a second exemplary embodiment.

FIG. 11 is a graph illustrating an example of power spectrumcharacteristics of a carrier wave signal output from the modulationdevice according to the second exemplary embodiment.

FIG. 12 is a timing diagram illustrating a detailed operation example ofa modulation device according to a third exemplary embodiment.

FIG. 13 is a circuit diagram illustrating a configuration example of apower amplifier.

FIG. 14 is a block diagram illustrating a configuration example of an Sphase clock converter circuit including signal selection circuit andphase interpolator.

FIG. 15 is a block diagram illustrating one configuration example of amodulation device according to a fourth exemplary embodiment.

FIG. 16 is a block diagram illustrating another configuration example ofthe modulation device according to the fourth exemplary embodiment.

FIG. 17 is a circuit diagram illustrating a configuration example of aduty converter circuit generating a pulse wave supplied to the poweramplifier of FIG. 13.

FIG. 18 is a timing diagram illustrating the operation of the dutyconverter circuit of FIG. 17.

EXEMPLARY EMBODIMENT

Hereinafter, the present invention will be described with reference tothe attached drawings.

First Exemplary Embodiment

FIG. 4 is a block diagram illustrating the configuration of a modulationdevice according to a first exemplary embodiment.

The modulation device according to the first exemplary embodimentincludes carrier signal generator 101 generating k carrier signalsCLK1˜CLKk having the same frequency fc and different phases, signalselection circuit 102 selecting two carrier signals CLK[i] and CLK[i+1]from carrier signals CLK1˜CLKk according to a phase modulation controlsignal (digital signal) and outputting selected carrier signals CLK[i]and CLK[i+1], phase interpolator 103 adjusting the phase in smallerunits than the phase difference between respective carrier signalsCLK1˜CLKk according to the phase modulation control signal andmodulating the frequency or the phase of the carrier signal into abaseband signal based on carrier signals CLK[i] and CLK[i+1] selected bysignal selection circuit 102 to generate a carrier wave signal, andphase modulation signal generation circuit 104 generating the phasemodulation control signal to control signal selection circuit 102 toselect two carrier signals CLK[i] and CLK[i+1] and phase interpolator103 to generate the carrier wave signal.

As illustrated in FIG. 4, the baseband signal and a phase switchingclock are input to phase modulation signal generation circuit 104. Inthis exemplary embodiment, a clock having the same frequency as carriersignals CLK1˜CLKk is used as the phase switching clock.

Phase modulation signal generation circuit 104 switches the phasemodulation control signal in synchronization with the phase switchingclock, thus switching the phase of the carrier wave signal in everyperiod. More specifically, phase modulation signal generation circuit104 outputs the phase modulation control signal corresponding to thebaseband signal at the rising timing of the phase switching clock,thereby switching the phase of the carrier wave signal output from phaseinterpolator 103 in every rising timing of the phase switching clock.

FIG. 5 is a circuit diagram illustrating a configuration example of thephase interpolator of FIG. 4.

As illustrated in FIG. 5, phase interpolator 103 may be implemented withthe combination of a well-known dynamic circuit and a constant currentsource circuit. The detailed configuration of the phase interpolator hasbeen described in above Patent reference 1.

Phase interpolator 103 of FIG. 5 sets ‘a’ control signals to a highlevel among N-bit control signals CT1[1], CT1[2], . . . , CT1[N], andthus can set a value of current flowing through transistor M1 to aI whencarrier signal CLK[i] has a high level.

Moreover, phase interpolator 103 of FIG. 5 sets b control signals to ahigh level among N-bit control signals CT2[1], CT2[2], CT2[N], and thuscan set a value of current flowing through transistor M2 to bI whencarrier signal CLK[i+1] has a high level.

Meanwhile, I indicates a current flowing through each constant currentsource circuit.

Here, the phase of carrier signal CLK[i] is delayed by a delay valuedetermined by a ratio of value al of the current flowing throughtransistor M1 to value bI of the current flowing through transistor M2.That is, as illustrated in FIG. 6, when time T equivalent to the phasedifference between carrier signals CLK[i] and CLK[i+1] is divided byb:a(a+b=N), phase interpolator 103 outputs a signal (carrier wavesignal) delayed from carrier signal CLK[i] by the time (b/N: a+b=N)×Tequivalent to b.

Control signals CT1[1]˜CT1[N] and CT2[1]˜CT2[N] may be generated using alogic circuit or the like based on the phase modulation control signaloutput from phase modulation signal generation circuit 104.Alternatively, control signals CT1[1]˜CT1[N] and CT2[1]˜CT2[N] may bethe phase modulation control signals output from phase modulation signalgeneration circuit 104.

Carrier signal generator 101 may be implemented with, e.g., a flip-flopwhich frequency-divides a clock signal having a higher frequency thancarrier signals CLK1˜CLKk. In addition, signal selection circuit 102 andphase modulation signal generation circuit 104 may be implemented withthe combination of a well-known logic circuit, a selector, etc.

FIG. 7 is a block diagram illustrating a setting example of phasemodulation control signals supplied to the signal selection circuit andthe phase interpolator of FIG. 4, and FIG. 8 is a timing diagramillustrating a detailed operation example of the signal selectioncircuit and the phase interpolator of FIG. 4.

As illustrated in FIG. 7, carrier signal CLK1 (phase=0°), carrier signalCLK2 (phase=360°×1/N) and carrier signal CLKN (phase=360°×(N−1)/N) areinput to signal selection circuit 102.

Signal selection circuit 102 selects two carrier signals CLK[p] andCLK[p+1] from carrier signals CLK1˜CLKN according to phase modulationcontrol signal p output from phase modulation signal generation circuit104 and outputs selected carrier signals CLK[p] and CLK[p+1]. Forexample, when phase modulation control signal p is ‘1’, signal selectioncircuit 102 outputs carrier signal CLK1 through a first output terminaland carrier signal CLK2 through a second output terminal. In addition,when phase modulation control signal p is ‘2’, signal selection circuit102 outputs carrier signal CLK2 through the first output terminal andcarrier signal CLK3 through the second output terminal. Moreover, whenphase modulation control signal p is ‘3’, signal selection circuit 102outputs carrier signal CLK3 through the first output terminal andcarrier signal CLK4 through the second output terminal. Likewise, whenphase modulation control signal p is ‘k’, signal selection circuit 102outputs carrier signal CLKk through the first output terminal andcarrier signal CLKk+1 through the second output terminal.

Here, when it is assumed that the phase modulation control signal inputto signal selection circuit 102 is p and when the phase modulationcontrol signal input to phase interpolator 103 is q, the phase of thecarrier wave signal output from phase interpolator 103 upon the input ofcarrier signal CLK1 is expressed as 360°/k×(p+q/N).

The phase resolution, which is a minimum delay value controllable by thephase modulation control signal, is 360°/(k×N). Phase interpolator 103outputs carrier wave signals having different phases in units of360°/(k×N) within the range of 0° to 360°.

In general, a wireless communication apparatus mostly adopts a phasemodulation method, in which, when a baseband signal (data) has a valueof ‘1’, a phase of a carrier wave signal increases at a fixed ratio inevery period of a carrier signal and reaches a phase (e.g., +90°equivalent to data ‘1’ after defined periods, and when the basebandsignal has a value of ‘0’, the phase of the carrier wave signaldecreases at a fixed ratio in every period of the carrier signal andreaches a phase (e.g., −90° equivalent to data ‘0’ after definedperiods.

The reason for this is to smoothly change the phase of the carrier wavesignal to the phase corresponding to data ‘1’ or ‘0’ in plural periodsbecause switching the phase of the carrier wave signal to +90° or −90°in units of one period increases spurious noise components unnecessaryfor the wireless communication.

In this exemplary embodiment, phase modulation signal generation circuit104 of FIG. 4 is operated by the phase switching clock having the samefrequency as the carrier signal, such that the phase of the carrier wavesignal increases or decreases in units of Δθ in every rising of thecarrier signal and reaches the phase corresponding to the value of thebaseband signal after the plural periods.

As described above, the frequency of the carrier wave signal increasesor decreases from frequency fc of the carrier signal by Δfc. Here, thefact that the frequency increases from fc to fc+Δfc indicates that theperiod becomes (fc/(fc+Δfc)) times. When the frequency becomes fc+Δfc,the period is shortened to 360°×(1−fc/(fc+Δfc))=360°×Δfc/(fc+Δfc).

Therefore, when k and N are set such that phase valueΔθ=360°×Δfc/(fc+Δfc) of the carrier wave signal with respect to thecarrier signal is an integer multiple of 360°/(k×N), the frequency ofthe carrier signal can be increased to fc+Δfc or decreased to fc−Δfc.That is, the modulation device of FIG. 4 may be used as the frequencymodulation device. In addition, when the frequency of the carrier signalincreases or decreases in units of Mc and reaches a target phase after adefined number of periods, the modulation device of FIG. 4 may be usedas the phase modulation device. FIG. 9 illustrates a phase modulationoperation example when it is assumed that k=8 and N=6.

In the conventional frequency conversion device of FIG. 2, the n phasegeneration circuit needs n phase interpolators such that the carrierfrequency becomes n/m times. Meanwhile, since the modulation device ofthis exemplary embodiment is implemented with one phase interpolator 103and one signal selection circuit 102 in which the switching step numberis N, the circuit area of the frequency modulation device or the phasemodulation device can be reduced. Moreover, since the modulation deviceof this exemplary embodiment uses fewer phase interpolators 103 than theconventional frequency conversion device of FIG. 2, it consumes lesspower.

Second Exemplary Embodiment

A modulation device according to a second exemplary embodiment isdifferent from the modulation device according to the first exemplaryembodiment in that a period of a phase switching clock is set to R timesa period of a carrier signal (a frequency is 1/R times) and in that aphase change value caused by phase interpolator 103 is increased morethan that of the first exemplary embodiment by R times (R×Δθ). Apartfrom this, the modulation device according to the second exemplaryembodiment is the same as the modulation device according to the firstexemplary embodiment, and thus detailed explanations thereof areomitted.

As described above, although the period of the phase switching clocksupplied to phase modulation signal generation circuit 104 is set to Rtimes the period of the carrier signal and the phase change value causedby phase interpolator 103 is increased more than that of the firstexemplary embodiment by R times (R×Δθ), as illustrated in FIG. 10, thephase change value obtained in every R period of the carrier signal isthe same as when the phase is changed by Δθ in every period of thecarrier signal shown in FIG. 8. Therefore, similarly to the modulationdevice according to the first exemplary embodiment, the modulationdevice according to the second exemplary embodiment may be implementedas a phase modulation device or a frequency modulation device.

Meanwhile, when the modulation device according to the second exemplaryembodiment is used in a wireless communication apparatus, frequencycomponents (fc×(1/R) components) of the phase switching clock may beleaked to the carrier wave signal. For example, the frequency componentsof the phase switching clock may be output from a power amplifier fortransmission. In this case, it is necessary to set a value of R tosatisfy the standard of the wireless communication apparatus using themodulation device of this exemplary embodiment (e.g., limiting the powerstrength except for predetermined frequency components to below −20dBm-40 dBm).

FIG. 11 illustrates an example of power spectrum characteristics of thecarrier wave signal output from the modulation device according to thesecond exemplary embodiment. FIG. 11 illustrates the example of powerspectrum characteristics of the carrier wave signal when the carrierfrequency is set to 2.4 [GHz] and when the frequency of the phaseswitching clock is set to 40 [MHz], i.e., R=60.

As illustrated in FIG. 11, in the case of the carrier wave signal outputfrom the modulation device according to the second exemplary embodiment,the peak of the power spectrum exists in a frequency that is differentfrom the carrier frequency by 40 [MHz] except for the power spectrum inthe frequency of the carrier signal.

However, according to the power spectrum characteristics of FIG. 11, thestrength of the power spectrum of the frequency that is different fromthe carrier frequency by 40 [MHz] should have a limit that is limitedlower than the power spectrum of the carrier frequency by more than 30[dB]. Therefore, a wireless communication apparatus pursuant to thewireless standard such as Zigbee, which places fewer restrictions on thestrength of the power spectrum other than the carrier frequency, may usethe modulation device according to the second exemplary embodimentwithout any problem. Meanwhile, it is prescribed in Zigbee that thestrength of the power spectrum other than the carrier frequency shouldbe set lower than the strength of the power spectrum of the carrierfrequency by 20 dB. As such, there is a margin over 10 dB using themodulation device according to the second exemplary embodiment.

A wireless communication apparatus, in which the strength of the powerspectrum other than the carrier frequency should have a limit that islower than the strength of the power spectrum of the carrier frequencyby more than 30 dB, can reduce an unnecessary peak of the power spectrumby, for example, spectrum-spreading a phase modulation control signaloutput from phase modulation signal generation circuit 104 by ΔΣmodulation, etc.

In addition, when the peak other than the carrier frequency is afrequency sufficiently that is different from a frequency of an adjacentchannel, since the limitation on the strength of the power spectrum isless strict, there may be used a method for decreasing the value of Rsuch that the peak of the power spectrum except for the carrierfrequency is different from the carrier frequency.

According to the modulation device of this exemplary embodiment, thefrequency of the phase switching clock is set to 1/R times the carrierfrequency, thus decreasing the operating frequency of phase modulationsignal generation circuit 104. As a result, the design of the phasemodulation signal generation circuit can be simplified and powerconsumption thereof can be reduced.

Moreover, while k and N values need to be set to switch the phase inunits of Δθ in the modulation device according to the first exemplaryembodiment, k and N values are set to switch the phase in units of R×Δθin the modulation device according to the second exemplary embodiment,such that the number N of constant current source circuits provided inphase interpolator 103 of FIG. 5 can be reduced into 1/R. As such, themodulation device according to the second exemplary embodiment canreduce the circuit area of phase interpolator 103 more than themodulation device according to the first exemplary embodiment. Further,since the number of the constant current source circuits decreases, themodulation device according to the second exemplary embodiment canreduce power consumption more than the modulation device according tothe first exemplary embodiment.

In the modulation devices according to the first and second exemplaryembodiments, the minimum period of the carrier wave signal is 1/fc butthe average period is 1/(fc+Δfc). Therefore, the modulation devicesaccording to the first and second exemplary embodiments are effectivelyused in the field in which the frequency spectrum determined by theaverage period strength is given more weight than the logic circuitdesign with the performance determined by the minimum period, andspecifically, used as phase modulation devices or frequency modulationdevices of the wireless communication apparatus.

Third Exemplary Embodiment

A modulation device according to a third exemplary embodiment is appliedto a phase modulation method which changes a phase of a carrier wavesignal from 360°×pa to 360°×pb with respect to a phase of a carriersignal, corresponding to a baseband signal having a period which is ktimes the period of the carrier signal.

In this case, a period of a phase switching clock is set to N1 times theperiod of the carrier signal (i is an integer from 1 to m, and N1, N2, .. . , Nm are an arbitrary integer combination wherein N1+N2+ . . .+Nm=k). That is, the modulation device according to the third exemplaryembodiment is different from the modulation devices according to thefirst and second exemplary embodiments in that the period of the phaseswitching clock supplied to phase modulation signal generation circuit104 is not limited to a fixed value and in that a phase change valuecaused by phase interpolator 103 is not limited to a fixed value. Thephase change value caused by phase interpolator 103 may be set such thata phase difference that is to be switched in every Ni periods of thecarrier wave signal becomes 360°×Ti (Ti is an arbitrary combinationwherein T1+T2+ . . . +Tm=pb-pa). Apart from this, the modulation deviceaccording to the third exemplary embodiment is the same as themodulation device according to the first exemplary embodiment, and thusdetailed explanations thereof are omitted.

Although the period of the phase switching clock supplied to phasemodulation signal generation circuit 104 is set to Ni times the periodof the carrier signal and the phase change value caused by phaseinterpolator 103 is set to 360°×Ti, as illustrated in FIG. 12, the phaseof the carrier wave signal obtained after k periods of the carriersignal can be changed from 360°×pa to 360°×pb. Accordingly, similarly tothe modulation devices according to the first and second exemplaryembodiments, the modulation device according to the third exemplaryembodiment may be implemented as a phase modulation device or afrequency modulation device.

Since the modulation device according to the third exemplary embodimentdoes not control the phase switching clock or the phase change valuecaused by phase interpolator 103 to a fixed value, it thereby reduces apeak value of the power spectrum of the frequency other than the carrierfrequency.

Fourth Exemplary Embodiment

As illustrated in FIG. 13, Japanese Patent Application No. 2006-250123filed for registration by the present applicants prior to the presentapplication suggests a configuration synthesizing a plurality of carrierwave signals having the same frequency, different ratios (duty ratios)of a high level time to a low level time of a signal voltage, anddifferent phases, thereby restricting harmonic components of the carrierwave signal output from a power amplifier for transmission.

A fourth exemplary embodiment provides a configuration example of apulse generation device including an S phase clock converter circuithaving S sets of the signal selection circuit and the phase interpolatordescribed in the first to third exemplary embodiments and outputting Scarrier signals having a phase difference of 360°/S, and a duty ratioconverter circuit generating S carrier wave signals (pulse waves 21-23)having different duty ratios in units of 1/S from the S phase carriersignals output from the S phase clock converter circuit.

As illustrated in FIG. 14; the S phase clock converter circuit includesS sets (6 sets in FIG. 14) of signal selection circuit 102 and phaseinterpolator 103 described in the first exemplary embodiment. Phasemodulation signal generation circuit 104 provides appropriate values tosignal selection circuits 102 and phase interpolators 103 as phasemodulation control signals, thus generating the S phase signals havingthe phase difference of 360°/S. For example, the phase modulationcontrol signals supplied to signal selection circuits 102 and phaseinterpolators 103 are set to values shown in FIG. 14 such that 6 phasesignals having phases of 0°, 60°, 120°, 180°, 240° and 300° aregenerated from 4 phase signals having phases of 0°, 90°, 180° and 270°.

The numerical values shown in signal selection circuits 102 and phaseinterpolators 103 of FIG. 14 indicate the values of the phase modulationcontrol signals supplied from phase modulation signal generation circuit104. The numerical values in signal selection circuits 102 areequivalent to p of FIG. 7, the upper numerical values in phaseinterpolators 103 are equivalent to q of FIG. 7, and the lower numericalvalues in phase interpolators 103 are equivalent to N-q of FIG. 7.

Meanwhile, as explained in the first and second exemplary embodiments,the S phase clock converter circuit of FIG. 14 can modulate the phasesof the entire 6 phase output signals. FIG. 15 illustrates thecombination of the phase modulation signals when the phases of theentire 6 phase output signals are faster by +15°. In addition, FIG. 16illustrates the combination of the phase modulation signals when thephases of the entire 6 phase output signals are slower by −15°. Ineither FIG. 15 or FIG. 16, the phase difference between the respectiveoutput signals is maintained as 60°. As described above, the phasemodulation control signals are appropriately set to maintain the phasedifference between the S phase output signals and modulate the phases ofthe entire S phase clock signals.

The duty converter circuit which generates pulse waves 21-23 havingdifferent duty ratios and supplied to the power amplifier of FIG. 13 maybe implemented with a logic circuit as shown in FIG. 17. The S phaseclock signals generated in the S phase clock converter circuit aresupplied to the duty converter circuit.

FIG. 18 is a timing diagram illustrating an operation example of theduty converter circuit of FIG. 17. FIG. 18 illustrates the operationexample upon input of 6 phase clock signals S1˜S6 generated in the Sphase clock converter circuit of FIG. 14.

As illustrated in FIG. 18, it is assumed that first signal S1 is pulsewave 21 having a duty ratio of 50%. A high level time of pulse wave 21is 0˜(½)×T0.

When second signal S2 and third signal S3 are input to the logic circuitof FIG. 17, a signal of pulse wave 23 (duty ratio is 100×(⅙) %) shown inFIG. 18 is output. A high level time of this waveform is (⅙)×T0˜(2/6)×T0.

Moreover, when fifth signal S5 and sixth signal S6 are input to thelogic circuit of FIG. 17, a signal of pulse wave 22 (duty ratio is100×(⅚) %) shown in FIG. 18 is output. A low level time of this waveformis ( 4/6)×T0˜(⅚)×T0.

Pulse waves 22 and 23 output from the duty converter circuit areamplified in first amplifier 202 provided in power amplifier 201 of FIG.13, and pulse wave 21 output from the duty converter circuit isamplified in second amplifier 203 provided in power amplifier 201 ofFIG. 13. Power amplifier (power amplifier) 201 outputs a syntheticsignal of the output signals of first amplifier 202 and second amplifier203.

The signal output from power amplifier 201 is emitted through antenna205 with unnecessary frequency components removed therefrom by band-passfilter 204.

According to this exemplary embodiment, since the carrier signals areconverted into the plurality of carrier wave signals using the S phaseinterpolators, it is possible to obtain the pulse waveforms through aconfiguration simpler than the configuration disposing a duty adjustmentcircuit after the generation of the carrier wave signal as disclosed inJapanese Patent Application No. 2006-250123. As a result, the circuitarea and the power consumption of the pulse wave generation device arereduced.

This application claims the priority of Japanese Patent Application No.2007-152723 on Jun. 8, 2007, the disclosures of which are incorporatedherein by reference.

1-5. (canceled)
 6. A modulation device for modulating a frequency or aphase of a carrier signal into a baseband signal, the modulation devicecomprising: a signal selection circuit selecting two carrier signalsfrom a plurality of carrier signals having the same frequency accordingto a defined control signal and outputting the selected carrier signals;a phase interpolator adjusting the phase in smaller units than a phasedifference between the plurality of carrier signals according to thecontrol signal and modulating the frequency or the phase of the carriersignal into the baseband signal based on the carrier signals selected bythe signal selection circuit to generate a carrier wave signal; and aphase modulation signal generation circuit generating the control signalthat is to control the signal selection circuit to select the twocarrier signals and the phase interpolator to generate the carrier wavesignal.
 7. The modulation device according to claim 6, wherein theplurality of carrier signals have the same phase difference.
 8. Themodulation device according to claim 7, wherein the phase modulationsignal generation circuit switches the control signal corresponding tothe baseband signal in synchronization with a phase switching clockwhich is the same frequency as the carrier signal to switch the phase ofthe carrier wave signal in every period, wherein, when the frequency ofthe carrier signal is fc and the modulation frequency is Δfc, a phasechange value that is to be switched in every period of the carrier wavesignal is 360°×Δfc/(fc+Δfc).
 9. The modulation device according to claim7, wherein the phase modulation signal generation circuit switches thecontrol signal corresponding to the baseband signal in synchronizationwith a phase switching clock which is a frequency 1/R times thefrequency of the carrier signal to switch the phase of the carrier wavesignal in every R period, wherein, when the frequency of the carriersignal is fc and the modulation frequency is Δfc, a phase change valuethat is to be switched in every R period of the carrier wave signal isR×360°×Δfc/(fc+Δfc).
 10. The modulation device according to claim 7,wherein, when i is an integer from 1 to m, N1, N2, . . . , Nm are anarbitrary integer combination, wherein N1+N2+ . . . +Nm=k, and Ti is anarbitrary combination, wherein T1+T2+ . . . +Tm=pb−pa, the phasemodulation signal generation circuit switches the control signalcorresponding to the baseband signal having a period k times the periodof the carrier signal in synchronization with a phase switching clock inwhich the carrier signal rises at every Ni times, wherein, when thephase of the carrier wave signal is changed from 360°×pa to 360°×pb withrespect to the phase of the carrier signal according to the basebandsignal, a phase difference that is to be switched in every Ni period ofthe carrier wave signal is 360°×Ti.
 11. A pulse wave generation devicecomprising: an S phase clock converter circuit including S sets o asignal selection circuit and a phase interpolator, as recited in claim7, and outputting S carrier signals having the same frequency and aphase difference of 360°/S; and a duty ratio converter circuitgenerating S carrier wave signals having different duty ratios in unitsof 1/S from the S phase carrier signals output from the S phase clockconverter circuit.